.. Objectives

.. ----------

.. By the end of this tutorial, you will be able to 

.. * Create sets from lists

.. * Perform union, intersection and symmetric difference operations

.. * Check if a set is a subset of other

.. * understand various similarities with lists like length and containership

.. Prerequisites

.. -------------

..   1. Getting started with lists

.. Author              : Nishanth Amuluru

   Internal Reviewer   : 

   External Reviewer   :

   Checklist OK?       : <put date stamp here, if OK> [2010-10-05]

Script

------

{{{ Show the slide containing title }}}

Hello friends and welcome to the tutorial on Sets

{{{ Show the slide containing the outline slide }}}

In this tutorial, we shall learn

 * sets 

 * operations on sets

Sets are data structures which contain unique elements. In other words,

duplicates are not allowed in sets.

Lets look at how to input sets.

type

::

    a_list = [1, 2, 1, 4, 5, 6, 2]

    a = set(a_list)

    a

We can see that duplicates are removed and the set contains only unique

elements. 

::

    f10 = set([1, 2, 3, 5, 8])

    p10 = set([2, 3, 5, 7])

f10 is the set of fibonacci numbers from 1 to 10.

p10 is the set of prime numbers from 1 to 10.

Various operations that we do on sets are possible here also.

The | (pipe) character stands for union

::

    f10 | p10

gives us the union of f10 and p10

The & character stands for intersection.

::

    f10 & p10

gives the intersection

similarly,

::

    f10 - p10

gives all the elements that are in f10 but not in p10

::

    f10 ^ p10

is all the elements in f10 union p10 but not in f10 intersection p10. In

mathematical terms, it gives the symmectric difference.

Sets also support checking of subsets.

::

    b = set([1, 2])

    b < f10

gives a ``True`` since b is a proper subset of f10.

Similarly,

::

    f10 < f10

gives a ``False`` since f10 is not a proper subset.

hence the right way to do would be

::

    f10 <= f10

and we get a ``True`` since every set is a subset of itself.

Sets can be iterated upon just like lists and tuples. 

::

    for i in f10:

        print i,

prints the elements of f10.

The length and containership check on sets is similar as in lists and tuples.

::

    len(f10)

shows 5. And

::

    1 in f10

    2 in f10

prints ``True`` and ``False`` respectively

The order in which elements are organised in a set is not to be relied upon 

since sets do not support indexing. Hence, slicing and striding are not valid

on sets.

{{{ Pause here and try out the following exercises }}}

%% 1 %% Given a list of marks, marks = [20, 23, 22, 23, 20, 21, 23] 

        list all the duplicates

{{{ continue from paused state }}}

Duplicates marks are the marks left out when we remove each element of the 

list exactly one time.

::

    marks = [20, 23, 22, 23, 20, 21, 23] 

    marks_set = set(marks)

    for mark in marks_set:

        marks.remove(mark)

    # we are now left with only duplicates in the list marks

    duplicates = set(marks)

{{{ Show summary slide }}}

This brings us to the end of the tutorial.

we have learnt

 * How to make sets from lists

 * How to input sets

 * How to perform union, intersection and symmetric difference operations

 * How to check if a set is a subset of other

 * The various similarities with lists like length and containership

{{{ Show the "sponsored by FOSSEE" slide }}}

This tutorial was created as a part of FOSSEE project, NME ICT, MHRD India

Hope you have enjoyed and found it useful.

Thank you!